As broadband networks such as Asymmetrical Digital Subscriber Line (hereinafter referred to as ADSL), Very-high-bit-rate Digital Subscriber Line (hereinafter referred to as VDSL), and Fiber To The x (hereinafter referred to as FTTx) (x represents the destination) rapidly develop, and the technologies and applications such as Voice over Digital Subscriber Line (hereinafter referred to as VoDSL) and Voice over Internet Protocol (hereinafter referred to as VoIP) are mature, the increased broadband rate and the improved network Quality of Service (hereinafter referred to as QoS) mechanism may ensure that the conversation quality of VoIP calls is equivalent to the conversation quality of Public Switched Telephone Network (hereinafter referred to as PSTN) calls. Since 2006, the global VoIP market develops rapidly, and the telecom operators gradually replace the traditional PSTN/Integrated Service Digital Network (ISDN) voice service by the VoDSL/VoIP voice service, and phase out the operation of the existing PSTN/ISDN network to reduce the Operating Expense (herein after referred to as OPEX).
However, in the process of implementing the present invention, the inventor finds that when implementing the VoIP telephone service, the IP-based broadband network and the IP Multimedia Subsystem (IMS) are vulnerable to connectivity failure, which may make the VoIP telephone service unavailable.
As a technical solution to the problem in the prior art, “PSTN/ISDN+VoIP” is adopted to implement the telephone service. However, the PSTN/ISDN network device is required to be preserved and maintained, and this increases the OPEX for the telecom operators. Therefore, a solution for implementing the telephone service without any PSTN/ISDN network device is desired.